A PCI Express connection provides a general purpose interconnect for computing and communicating platforms. PCI Express components communicate over a point-to-point communication channel known as a link that provides a high speed, serial connection between the PCI Express components. Packets, such as Transaction layer packets (TLPs), are communicated over the link according to the PCI Express protocol.
In addition to the high speed signals communicated via the PCI Express link, sideband signals can also be communicated between PCI Express components. A sideband signal is a physical signal that is separate from the signals forming the main link between two PCI Express components. Thus, the PCI Express protocol provides a method for signaling events and conditions using physical signals separate from the signals forming the link between two PCI Express components. The WAKE# mechanism is an example of a sideband signal used in the PCI Express protocol to implement wakeup functionality.